1. Field of the Invention
This invention relates to treating subsurface layers of earth adjacent, or near, the surface to reduce the volume change potential of clayey and silty soils and to build strength of the subsurface layers. More particularly, this invention relates to improving the subgrade; as for buildings, roadbeds, and the like.
2. Description of the Prior Art
The prior art is replete with a wide variety of materials that have been employed to stabilize soils, or improve subgrades in the subsurface layers adjacent the surface of the earth for a variety of purposes. The applications have been as varied as improving subgrades for building sites, streets, runways, railroads, dewatering projects and more recently, improving the slopes for preventing failure thereof. Of course, pretreating building sites for improving the strength and volume change characteristics of soils has long been a problem plaguing the civil engineer and the architectural engineer. The problems have been varied and the techniques have been varied to try to overcome them. Lime slurries have been worked into the top layers; for example, the top 6-36 inches in depth to improve and stabilize soils or subgrades. Other more exotic and expensive treatment, such as injection of furfural alcohols, that have been found to work in subterranean formations, have been tried. Such exotic treatments have proven too expensive and not altogether successful because the lack of metamorphosed rock in the subsurface layers adjacent the surface of the earth. Expressed otherwise, these exotic treatments were infeasible and engineeringly inoperable; because numerous small cracks, crevices and the like traversed through soil and because the soils were composed largely of sedimentary materials, amorphous materials, humous matter, non crystallographic materials and the like, that could not be consolidated as were the subterranean formation.
Chemical soil stabilization by injection of slurry has been a recent (last 15 years) development using slaked, or hydrated, lime, with or without additional material. Exemplary of such additional materials is the use of fly ash such as disclosed in our U.S. Pat. No. 4,084,381, issued Apr. 18, 1978 and entitled "Stabilization of Earth Subsurface Layers"; and the details of that patent are incorporated herein by reference for details that are omitted herefrom.
Two of the principle applications of this system are the stabilization of railroads and building sites, although the injection of the lime slurry has become increasingly more widely used in slope stabilization, landfill stabilization, dewatering, runway and street stabilization and remedial stabilization of existing structures, as by lifting foundations or the like.
Since the advent of the energy crisis, the price of hydrated lime has risen dramatically. Moreover, prices continue to rise steadly as this is a highly energydependent product. Furthermore, in certain parts of the United States, difficulty is frequently experienced in obtaining adequate quanities of hydrated lime (calcium hydroxide).
Thus it can be seen that the prior art has not been totally satisfactory in providing an economical process in which the starting materials were always available at an economical price.
One of the deficiencies of the prior art also has been the injection of the lime slurry, with or without additives in cold weather, or during the winter season, when ambient temperatures would cause the slurry to freeze either in the mixing tanks, conduits or pumps and the cold slurry would not react readily with the soils because full and final chemical reactions are temperature dependent.